Debian is an Operating System which uses the Linux kernel. Though it is usually installed on desktop computers, it is being used on a growing number of web servers too. The reason is that it is really stable, so a server running it won't have to be restarted for months. Debian is also considered to be one of the most secure Operating Systems out there, because security patches are released within days after an issue is discovered. This is possible because thousands of well-trained developers work for the Debian project on a voluntary basis and not only do they work on the OS itself, in addition, they provide 24/7 support by using special mailing lists and respond in twenty minutes to any kind of question. Thus, you will get an outstanding level of support directly from the developers who know their own platform in detail, and not from a third-party support team. Debian is also one of the Linux distributions with the highest number of packages - more than 30,000. Since the Operating System is free to use, you are able to modify both the core and all the packages in the way you see fit. Also, you will not need to pay any kind of license fees.